1. Field of the Invention
This invention relates to an attachment for use with an overhead door having limited headroom and made of hingedly connected sections.
2. Description of the Prior Art
Overhead doors for garages and warehouses and the like are well known. Generally speaking, the doors are made up on hinged sections, each section having a bracket extending from it to which is attached a roller member. The roller member engages in a track that is made up of a vertical section, substantially parallel to the door when the door is closed, a horizontal section, substantially parallel to the ground, in which the door rests when it is fully opened and a curved portion joining the vertical and horizontal portions. Typically, these doors have counterweights to facilitate their opening. Generally speaking, a wire rope is attached to the bottom of the door, runs upwardly, over a cable drum and downwardly to attach to a counterweight. In a typical domestic garage door there are two counterweights, one on each side of the door. Generally speaking, the combined weight of the counterweights is slightly less than the weight of the door. When the doors are closed the counterweights are raised. Thus, relatively slight pressure applied by hand to the door overcomes the difference in the weight of the door over the counterweight and the door can be lifted by hand easily. As the door is lifted the roller members attached to each section move upwardly in the vertical portion of the track, around the curved portion of the track and along the horizontal portion of the track.
Torsion springs are also widely used to reduce the opening effort. These are also used with a cable drum.
A problem is encountered with overhead doors having limited headroom. By limited headroom is meant that there is relatively little space between the upper edge of the upper section of the door and the roof of the garage. The cable drum is generally fitted in this space. With limited headroom the well known problem is that the upper section of the door hits against the cable drum if the distance between the upper section and its roller--engaged in the track--is greater than the distance between the lower surface of the drum and the track. This problem comes about because the roller of the upper section must engage in the track where is starts to curve away. Thus, the bracket upon which the roller for the top section is mounted must be fairly long. With adequate headroom it is not necessary to have an excessively long bracket. The track can be designed so that the curve in the track does not start until after the part of the track engaged by the upper section roller when the door is closed.
A number of devices have been designed to overcome the above disadvantage with overhead doors having limited headroom. The most popular method is to use a separate track just for the roller of the upper section. The separate track is generally disposed parallel and above the horizontal portion of the existing track that engages the rollers for the remaining section of the door. But the separate track only curves down gently at its end and finishes in the vicinity of the upper section of the door in such a way that the upper section can be provided with a roller on a fairly short bracket, in particular a bracket shorter than the distance between the cable drum and the track. The effect of the separate track is to ensure that the upper section immediately starts to move towards horizontal position upon opening of the door.
However the incorporation of an additional track and its mounting is clearly an expense.